1. Field
The disclosed embodiments relates to communication systems, and more particularly to a system and method for adjusting quality of service in a communication system.
2. Background
Various techniques are used to provide multiple access communications services to remote stations. One technique used is frequency division multiple access (FDMA). A base station implementing an FDMA scheme assigns a separate frequency band to each remote station. Each remote station transmits using a frequency band assigned by the base station at call setup time. Another technique used is time division multiple access (TDMA). A base station implementing a TDMA scheme assigns multiple remote stations to the same frequency band, but breaks that band into time slots and assigns slots to each remote station. Another multiple access technique, code division multiple access (CDMA) uses spread spectrum communications. Each remote station communicates on a common frequency band at the same time, but their transmissions are encoded using orthogonal codes such as Walsh codes. Because the codes are orthogonal, transmissions from one remote station have the effect of white noise on another remote station. Each of these techniques employs a shared resource that is allocated among multiple remote stations.
Quality of service in a wireless communication system can be represented in terms of data rate, frame error rate, or other signal characteristics. Generally, a higher quality of service can be provided to a particular remote station at a particular time only at the expense of increased consumption of a system resource such as system capacity. For example, increasing the quality of service to one remote station in a multi-user wireless communication system often means that there will be less system capacity available for providing increased quality of service to other remote stations in the system.
In any communication system in which resources are shared, if all communicating stations are assigned the same quality of service but the efficiency of the stations varies, the result is an inefficient allocation of the resource. Lower quality stations consume a disproportionate share of the resource because they need more of the resource to obtain the same quality of service as a higher quality station. Thus, a shared resource might have enough capacity to support a large number of efficient stations, but only a small number of very inefficient stations.
Where a communication system includes a combination of efficient and inefficient stations, a few inefficient stations might consume the entire shared resource. For example, in a CDMA system, transmissions from base stations to remote stations (in a direction referred to as the forward link) occur within a shared frequency band. Transmissions from remote stations to base stations (in a direction referred to as the reverse link) occur within another shared frequency band. When a lower quality remote station requires base stations to transmit forward link signals at a higher power level, this higher power level causes those forward link signals to consume greater forward link system capacity. Likewise, when a lower quality remote station must transmit reverse link signals at higher power, those reverse link signals will consume greater reverse link system capacity. The extra capacity consumed as a result of operating inefficient remote stations in the system decreases the overall number of remote stations that can be supported within the system. In a system that utilizes active power control, the remote station transmits and receives signals at the greatest power near the edge of coverage or at the “handoff boundary” between base stations. Consequently, an inefficient remote station causes the worst loss of system capacity when operating near the boundaries of coverage between base stations.
As a result of the inefficiencies created by lower quality remote stations in conventional systems, CDMA service providers have been reluctant to support remote stations that support subscriber information modules (SIMs). A SIM, also called a “smart card,” is a module that plugs into any of a variety of remote station brands and models. The SIM contains data that identifies a specific user account with a service provider. The remote station into which the SIM is plugged gets the service accorded thereto by the user account assigned to the SIM. A specific phone number is assigned to a SIM, not to a phone. A user may change the phone number of a remote station by exchanging one SIM for another. Additionally, a SIM may contain other attributes of the user account, such as billing parameters, an authorized set of types of service, or other aspects of service.
In essence, when a service provider sells a customer a SIM instead of a remote station, the service provider loses the ability to choose the make and model of the remote station that the customer uses on the system. Consequently, the service provider also loses control over the quality and efficiency of the remote stations operating on the system. Service providers fear that users will choose inexpensive remote stations that will ultimately degrade the quality of service or capacity of the system.
Many service providers do allow operation of SIM-capable remote stations on their systems. Such service providers may require their subscribers to select from a specific set of remote station models for which the system is optimized or which are known to operate efficiently. While this approach may maximize the efficiency of the system, it impinges on the customer's freedom to choose a remote station model. Often, the more efficient remote stations will cost more than the less efficient ones. Thus, limiting the customer's choices to only more efficient remote stations may raise the price barrier to entry for potential new customers. There is therefore a need for an approach which allows customers to choose from a greater selection of remote stations without sacrificing system efficiency and capacity.